Aligning TV Aerials & Antennas | Tips & Advice

March 13, 2019

by

Tom Smart

How To Align A TV Aerial

If you’re intending to install your own TV aerial to save
yourself a few pounds or dollars. One thing you will need to do for the TV to
work properly is to align the TV aerial. This isn’t always as simple as it
sounds and let this blog help you do it, together with tips and advice on how
to get maximum signal strength from your aerial.

I will begin by just saying that installing aerials can be
described as a bit of a black art. I mean nothing sinister by this of course
just that what works fine in one area may not work in another. I have
encountered many situations where aerial signals can be dramatically improved
by only moving the aerial fixing position a metre of two away from the original
fixing position. This means that what works for other properties in your area
might not necessarily work on yours. Of course, if your neighbour is getting a
reliable TV signal then chances are you should expect to also, but don’t take
this for granted. I have on occasion installed a TV aerial on one side of a
chimney only to find that it would only work on the other side of the same
chimney! I have also had when testing with my aerial alignment tool a TV aerial
not work on a chimney but work fine within a loft space, which good aerial
installation practice would contradict. Hence the “Installing aerials is a
black art!”.

Before fixing an aerial in a position and trying to align to
the best TV transmitter in your area I recommend first funning a signal test to
confirm that it is a suitable position to fix your TV aerial, I use a Promax HD
Ranger Spectrum analyser, but I appreciate that most people reading this blog
will be aligning their TV aerials DIY and going out and spending a few thousand
pounds on test equipment would defeat the object of doing the alignment
yourself, it would be cheaper to call a TV aerial company out. But if you are
going to be this regularly or semi regularly good alignment tools can only set
you back a couple hundred of pounds but could save you hours pointing your aerials.

If you’re interested on aligning satellite dishes. I have
already written another blog on how to align satellites dishes and I recommend
that you read that after this one if you need help with that.

How To Pick The Right TV Transmitter

One thing you need to do before you install your aerial is
to determine which direction that your aerial needs to be pointing. There are a
few things that you can quickly use to identify your optimum TV transmitter in
your area and these are:

Neighbours TV Aerial

By looking at your neighbours’ TV aerial you should get an
idea which way your TV aerial should be aligned. This can also help identify whether
you are in weak, average or strong signal area. Weaker signal areas tend to
have larger masts in which the antennas are mounted to help receive a stronger
signal higher up above the property where signals are typically less affected
by buildings and trees. Weak signal areas also tend to have far larger high
gain aerials to maximise the signal strength where it otherwise may be too
weak. If you notice that a lot of your neighbour’s TV antennas have small boxes
on the aerial pole which the coaxial cable runs in and out of, there’s a chance
that this is a masthead amplifier which has been installed to amplify or
“boost” a weak TV signal. Strong signal areas will on the other hand tend to
have a far smaller average TV aerial size mounted onto smaller masts. Another
telling sign that you’re in a strong signal area would be if you could see no
external TV aerials or very few on your neighbouring buildings. This could be
because there is adequate signal strength to install the aerials themselves in
the lofts of your neighbour’s properties. The upside of doing this of course is
that the aerial will receive no weathering so is much likely to fail and will
last a lot longer than an externally mounted aerial, I mean it isn’t exactly
going to blow down in a gale now is it? This isn’t always ideal or possible as
the signal will be weaker inside your loft however, so it’s not recommended 9
times out of 10.

If you notice a common theme with all your neighbour’s
aerials all pointing one way, then most likely that is the direction that you
need to point your antenna. If you notice that your neighbour’s aerials are all
pointing different directions, then there is a good chance that you live in a
fringe reception area and you will have to choose which transmitter to point
your aerial to. There could also be another reason that aerials in your area
are pointing different directions. Another common reason since the digital
switchover which saw 4 or 5 analogue channels removed to provide extra digital
TV services is that not all TV transmitters offer the same amount of services.
There could be a small local transmitter to you which may be the strongest in
your location but only offers a far smaller range of services called Freeview
Light, which is around half of the full Freeview service. It could be that many
of your neighbours to get a full Freeview service have aligned their aerials to
another transmitter, usually a main transmitter to get a full Freeview service.
This may even require an aerial replacement, or a higher gain TV aerial do you
should do your homework on transmitters in your area and the services they
offer before you point your aerial to them.

I will just finish this section by saying that by assuming
that everything is correct, fine and dandy with your neighbour’s aerials would
be a mistake. There is a chance that their aerial doesn’t work properly, and
they may not even be aware of this if they have satellite TV. If you can’t see
any aerials also do not assume that you are in a strong signal area as the must
be in their lofts. They may not have an aerial at all or they may be a covenant
in place prohibiting the erection of external antennas, vey common in new build
estates and listed buildings. Remember that your neighbours’ aerials should
only be used as a rough guide, especially if they themselves have installed the
aerial themselves as it may not be 100% in the correct position anyway.

Transmitter Postcode Checker

To quickly identify what transmitter, you should be using to
align your TV aerial to you can use an online postcode checker to do this for
you and I recommend this one. You just input your postcode and house number,
click check and it will come back with the most likely transmitter or use or
the intended transmitter of use in your area, together with information on how
many services you can expect to receive and TV packages available. I will say again that this should only be used
as a guide as there are some many variables that a simple postcode checker will
not be able to take into a consideration. I have had people argue with me until
they are blue in the face that they were using one transmitter when they were
in fact using another because of the results that the postcode checker had
given them. The postcode checker will not take into consideration any
obstructions like trees and nearby buildings which could be blocking your TV
signal for example.

An example in our neck of the woods in East Sussex. Are
places in the coast around Bexhill where the postcode checker will tell you to
use the Hastings transmitter, although you will get a full Freeview service
from this transmitter you could run into problems with interference from a
transmitter in Eastbourne which uses some of the same frequencies. This causes
co-channel interference which is where too different signals clash on the same
frequency and the signal get’s ruined. There is only one way around this as you
can’t filter the interfering signal out without filter the signals that you
want to keep. The only alternative would be to put up with poor digital TV
reception or try to align your TV aerial to a different transmitter like the
Heathfield transmitter. I have used this an example but each area in the UK
will have its own signal related challenges and a helpful local aerial
installer to you should be able to advise you on these.

UK Free TV Website – Information on TV Transmitters

Once you have an idea of what transmitter you’re going to be
using. I recommend quickly checking for more information on that transmitter to
see what frequencies it uses and to see whether it broadcasts a full Freeview
service or a limited Freeview Lite service.

I regularly use this website to get information on
frequencies and UHF channels, so I can manually tune TV’s (A much better way
than auto-tuning) and to help me pick the right aerial for the job. This helps
me design aerial systems and is particularly important if I intend to install a
grouped aerial which can offer performance benefits over wideband aerials which
are most commonly installed nowadays. The website will also tell you whether
the transmitter broadcasts on a horizontal or vertical polarisation which is
very common and something I will come to later.

Here is a link to the UK Free TV Site.

About The Aerial

There are a few things that you should be aware before you
try to align a TV aerial. The most important is whether the aerial you are
aligning is actually compatible with the transmitter you are aligning to. It
goes without saying, that although you may pick up some form of signal from
them. A FM or DAB radio aerial is not going to work properly when trying to
align a radio aerial for TV signals to a TV transmitter and neither with a
satellite dish. Another very important thing which you may not be aware of is
that some aerials are only tuned to pick up a smaller range of frequencies
within the UHF making them not compatible with all transmitters, these are
called grouped aerials. Here are the differences between grouped aerials and
wideband aerials.

Grouped Aerials

-
Will only pick up a small amount of the UHF

-
Better for signal reception and gain when using
correctly

-
Can help reduce interfering signals

-
Not compatible with all transmitters

-
Do not allow for broadcast changes which may see
transmitters broadcasting on frequencies outside scope of the grouped aerial

Wideband aerials

-
Work across the whole UHF

-
Less signal gain that grouped aerials

-
Not good for reducing unwanted out of band
signals

-
Compatible with all transmitters

-
Will allow for broadcast changes, so more future
proof.

Going forward it is most common for aerials that are
installed to be wideband aerials. 99% of the aerials we install now are
wideband models and as more and more of broadcasting space is being lost to
mobile broadband services like 4G and 5G some of the benefits that grouped
aerials are being eroded away. You can also install bandpass filters on a wideband
aerial to allow a smaller range of frequencies through.

Polarisation

If you are going to successfully align your antenna. It’s
absolutely crucial that you get the polarisation correct when mounting the
aerial onto the aerial pole. All transmitters broadcast on either a vertical or
horizontal polarisation with a very, very small amount of exceptions that use
both. This means that once you have identified the correct polarisation of the
transmitter you are using from UK Free TV to need to mount your antenna
accordingly. To mount for signals on a vertical polarisation the elements will
need to point up and to mount for signals on a horizontal polarisation the
elements will need to be pointing from side to side. I cannot stress how
important it is to get this right as to get it wrong would result in a
dramatically weaker signal. It may not seem that important, but it is. For
various reasons it’s common to re-align TV aerials from the Hastings
transmitter to the Heathfield transmitter in my location, you can often tell
who have done this “DIY” as they have just turned the mast around and made no
adjustment to the polarisation which is essential. This will result in a very
poor signal, probably poorer than before you moved the aerial to improve the reception.

There is a video on our Youtube channel which describes this
better. Click this link to see how to get your polarisation correct on your
aerial. A rough guide most main transmitters broadcast in a horizontal
polarisation and relay transmitters a vertical.

Acceptance Angles

An acceptance angle is the range of movement in degrees that
the aerial can be rotated before the signal gain halves. Minor adjustments to
aerial very rarely make a difference in regard to actual viewing experience and
pixilation unless you are in a poor signal area and every last dB counts. The
better the aerial you’re using and the higher the gain the more accurate you
need to when aligning your TV aerial as the acceptance angles are far narrower
giving you a smaller opportunity to get the aerial aligned for peak reception.

It’s common for people who are installing their own aerials,
“DIY” to buy a higher gain aerial than is necessary to get away with the fact
that they won’t know if the aerial is 100% aligned in the correct position. You
would need an alignment tool to be able to do this and the TV picture itself is
little help. What they are often doing in some situations is actually making
their installation much harder than it needs to be. Standard aerials or lower
gain aerials would be easier to install in medium to strong signal areas as you
won’t need to be as accurate with the antenna to peak a signal.

Aerial Aligning Tools

There are a few things which can make your aerial alignment
easier still. The big one would be a professional alignment tool. As I already
mentioned the equipment I use costs thousands, but you can get usable equipment
for a few hundred pounds or you may even be able to pick up a better model
second hand on the internet. If you’re going to buy a metre I recommend that it
has the following functions.

Bit error ratio readings to confirm that it is working, once you understand
this it will tell you show much more than the TV picture itself

DVB T Compatibility – This the main modulation used for TV aerial signals like
Freeview.

Also beneficial:

DVB T-2 Compatibility – This is a more
efficient compression technique as most commonly used for HD broadcasts. If you
are doing Soarview installations in Ireland than I recommend getting this as a
minimum as Soarview only uses DVB-T 2 and not DVB-T.

Demodulation – This will allow
your equipment to display a TV picture, which is nice but not important if you
understand MER readings and BER’s.

Google Maps

You can use this just to help find your property and the
transmitter you’re using. If you can use nearby landmarks you should be able to
point your aerial in the right direction. Just beware that as because TV aerial
signals are broadcast from land-based transmitters with potential obstructions
in the way sometimes the strongest signal is achieved by pointing the aerials
off the actual direction, this is because radio waves can bounce of buildings
and land masses like hills.

Aerial Alignment Smart Phone Apps

There are now loads of apps available on Apple iPhones and
Android compatible devices that will tell you which way to point your aerial
when you hold the phone up. This works by using your correct location, compass
and bearing to your nearest transmitter which is usually a selectable option
within the application itself. Some of the apps really are hit and miss and
they won’t give you signal strength or reliability readings but can be used as
a quick guide to identify a rough aerial direction.

Tips For Aligning Aerials With An Alignment Tool/ TV Analyser

When aligning your TV aerial using some sort of alignment tool
which allows you to see the UHF spectrum. There are a few things that you should
look to optimise. If you’re not using a meter to align your TV aerials, then
you are doing the installation blindfolded. You may get away with it a few times,
but you will get caught out with the TV not working properly sooner or later. I
know a few installers that could do with learning that!

Signal Strength

This is measured in dB. You should aim to maximise the
signal reading on all of the frequencies in use. As most digital TV transmitters
broadcast on 6 or 7 different frequency groups called multiplexes, Freeview Light
transmitters only have three. Separate readings should be taken of each of
these to ensure that you will achieve a good reliable signal on all TV
services. Some transmitters will broadcast some of these groups at a weaker
strength, like the Crystal Place transmitter does for local TV so there is a
chance that, so channels will be weaker than others. There are other scenarios
which can cause some of the multiplexes to be received fine and others weak or
poor like when signals pass through trees. Trees can cause all sorts of
problems with radio waves and should you should try to avoid pointing your
aerial through them. For your reference the minimum signal at the TV side of
the coaxial cable should be at least 50dB and the maximum no more than 80dB. If
this is the first time that you have heard of a maximum signal, yes there is
such a thing too much signal. Always get a strange look when I have told
someone this who has heard it for the first time. In practice aerial signals
can still work slightly above of below these signal levels but you should
strive keep them within these figures ideally around 55-70dB. Too much signal is
also why you shouldn’t install high gain TV aerials in strong signal areas and
if you have too much signal this can be remedied by installing an appropriate
sized attenuator before the aerial signal connects to any equipment to drop the
signal down to an acceptable level.

Signal Quality – MER – C/N

As well as maximising the signal strength you should look to
maximise the signal quality or the signal robustness. This is a reading usually
given in a Carrier to Noise ratio (C/N) but a Modulation Error Ratio (MER)
reading is more accurate for digital TV. They are both slightly different, but
the idea is the same, the C/N ratio is a reading between the signal strength and
the signal noise, there has to be an acceptable gap for reliable TV reception. Ideally,
you’re looking for a reading of more than 30dB but the suggested minimum for
digital TV is around 25dB. I won’t go anymore in this here as this depends on
compression techniques uses and will be a whole separate lengthy subject for
another blog on another day.

Flat Multiplexes

When looking at the multiplexes on your analyser these should
be as flat as possible and not bounce around. If you multiplex slopes to one
side or drops in the middle this is something that we say is “degraded” and you
should look to get these as level as possible even it means aligning the TV
aerial for a little less strength, on all the frequencies used as it could cause
poor TV reception.

Peak/ Drop/ Peak/ Drop

When you’re actually in the process of rotating your TV
aerial and watching the response on your aligning tool. You should look to point
the aerial roughly in the right direction. Rotate one way so that you see the
signal drop off considerably. Then rotate back the other way so that you see it
peak, when you see it peak continue rotating the same direction until you see
it drop off again. Then align to where the strongest position. This will help
you achieve the strongest signal and avoid any signal bounces that may have
picked up inadvertently instead of the actual signal.

Aerial Alignments East Sussex

If you need this provided for you and you are based in East
Sussex, West Sussex or South Kent then will would be delighted to do this for
you. Please do contact us today to book in your professional aerial alignment.

That’s it! What a blog, over 3500 words which I hope you found
helpful. As always if you have any questions that you would like to answer
please do LEAVE A COMMENT in the section below and I will get back to you in
the soonest. I would much prefer that you leave a comment instead of e-mailing
for technical questions as everyone reading the blog will get the benefit of
the question and answer. Of course, if you want to book you aerial alignment in
or any other aerial and satellite work please feel free to e-mail or call in!

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